發(fā)布時(shí)間：2018-05-11 12:19

  本文選題：低合金耐磨鋼 + 微合金化　； 參考：《中國科學(xué)技術(shù)大學(xué)》2016年博士論文

【摘要】：為了提高生產(chǎn)效率和降低制造成本,鐵礦粉生產(chǎn)線關(guān)鍵裝備及其工作部件不斷大型化。其中,耐磨襯板是鐵礦粉生產(chǎn)線關(guān)鍵裝備——磨機(jī)的核心工作部件,其使用壽命直接影響整條鐵礦粉生產(chǎn)線的運(yùn)行效率和制造成本。然而,目前國內(nèi)尚未形成超大型磨機(jī)的自主選材規(guī)范,致使我國超大型鐵礦粉生產(chǎn)線項(xiàng)目的主要關(guān)鍵設(shè)備完全依賴進(jìn)口,造成項(xiàng)目成本和進(jìn)度受制于人。為了達(dá)到預(yù)期設(shè)計(jì)使用壽命,大型耐磨部件選材在具有較高硬度和強(qiáng)度的同時(shí),應(yīng)當(dāng)具有優(yōu)異的韌性和塑性以及良好的淬透性。因此,如何獲得良好的強(qiáng)韌性匹配以及淬透性,進(jìn)一步提高耐磨鋼的耐磨性能,一直是研究者非常關(guān)注的課題。本文通過Ti、B和RE多元微合金化處理,設(shè)計(jì)了一系列新型中碳低合金耐磨鋼,分析了Ti、B和RE對(duì)微觀組織演變的影響,系統(tǒng)研究了在凝固和熱處理過程中含Ti析出相和稀土夾雜物的類型、尺寸和分布,及其對(duì)組織和力學(xué)性能的影響,探討了實(shí)驗(yàn)鋼的磨損機(jī)理以及Ti和RE微合金化、力學(xué)性能與耐磨性能之間的關(guān)系。在此基礎(chǔ)上,結(jié)合生產(chǎn)實(shí)際,實(shí)現(xiàn)了自主設(shè)計(jì)中碳低合金鋼耐磨襯板鑄件的批量化生產(chǎn),為我國低合金耐磨鋼的材料開發(fā)積累了寶貴經(jīng)驗(yàn),同時(shí)也為高品質(zhì)耐磨部件的應(yīng)用奠定了堅(jiān)實(shí)的理論基礎(chǔ)。本文的主要研究內(nèi)容包括：(1)結(jié)合熱力學(xué)計(jì)算和實(shí)驗(yàn)研究,提出了Ti、B和RE多元微合金化思想：通過微量B提高淬透性；加入適量Ti與鋼中N結(jié)合,確保B對(duì)淬透性的作用,并且形成TiN析出相,細(xì)化組織;加入適量RE(La、Ce),凈化鋼液、改善夾雜、細(xì)化晶粒。由此,設(shè)計(jì)了新型中碳低合金耐磨鋼合金體系。(2)采用熱膨脹儀測(cè)定了實(shí)驗(yàn)鋼的連續(xù)冷卻轉(zhuǎn)變(CCT)曲線,分析了Ti、B和RE多元微合金化對(duì)淬透性的影響。結(jié)果表明,實(shí)驗(yàn)鋼中,單獨(dú)加入B元素時(shí),B易與鋼中N結(jié)合,形成BN,嚴(yán)重削弱對(duì)淬透性的作用；并且,過量的B將促進(jìn)M23(C,B)6型碳化物沿晶界析出,反而降低鋼的淬透性。在此基礎(chǔ)上,加入適量的Ti元素,能夠有效固N(yùn),形成TiN析出相,抑制BN的產(chǎn)生,有利于發(fā)揮B顯著提高淬透性的作用。然而,實(shí)驗(yàn)鋼中加入RE元素,主要與鋼液中O、S結(jié)合形成RE203和RE202S稀土夾雜物,對(duì)鋼的淬透性基本沒有影響。(3)通過固液兩相區(qū)保溫凝固和連續(xù)冷卻凝固實(shí)驗(yàn),研究了實(shí)驗(yàn)鋼中TiN和稀土夾雜物的析出行為及其對(duì)凝固組織的影響。研究結(jié)果表明,等溫凝固和水淬冷卻后,實(shí)驗(yàn)鋼中的TiN和稀土夾雜物主要分布于凝固組織的粗大枝晶間、枝晶前沿和最后凝固的等軸晶晶界處,少量分布于凝固組織的粗大枝晶和等軸晶內(nèi)。低倍組織對(duì)比表明,加入Ti和RE元素,能夠顯著提高等軸晶比率,細(xì)化凝固組織。(4)系統(tǒng)研究了熱處理后實(shí)驗(yàn)鋼中含Ti析出相和稀土雜物的析出特征,并探討了Ti、RE含量對(duì)晶粒尺寸和力學(xué)性能的影響。結(jié)果表明,隨著Ti含量增加,實(shí)驗(yàn)鋼中含Ti析出相顆粒尺寸增大、析出含量增多,析出相類別逐漸轉(zhuǎn)變?yōu)槲⒚准?jí)的Ti(C,N)和納米級(jí)的(Ti,Mo)(C,N),具有明顯的彌散強(qiáng)化、細(xì)晶強(qiáng)化和韌塑性改善作用。當(dāng)Ti含量為0.021%時(shí),實(shí)驗(yàn)鋼綜合力學(xué)性能最佳;隨著Ti含量進(jìn)一步增加,含Ti析出相在凝固初期形核并快速長大,導(dǎo)致析出相的顆粒尺寸和析出量明顯升高,嚴(yán)重降低鋼的沖擊韌性。單獨(dú)加入適量RE元素時(shí),RE元素與鋼液中的O、S結(jié)合,生成絕大部分小于1μm的RE2O3和RE202S稀士夾雜物,有效起到凈化鋼液和變質(zhì)夾雜的作用,可以小幅提高鋼的沖擊韌性；但是,當(dāng)RE元素與Ti元素復(fù)合微合金化時(shí),稀土夾雜物極易作為鋼中TiN的有效形核核心,促使TiN與其形成尺寸較大的微米級(jí)復(fù)合類型析出相,造成沖擊韌性降低。(5)利用MLD-10型動(dòng)載磨料磨損實(shí)驗(yàn)機(jī),探討了實(shí)驗(yàn)鋼在沖擊磨料磨損條件下的磨損機(jī)理,以及Ti和RE微合金化、力學(xué)性能與耐磨性能之間的關(guān)系。實(shí)驗(yàn)結(jié)果顯示,在沖擊磨料磨損條件下,實(shí)驗(yàn)鋼磨損表面,除少量的顯微切削磨損外,主要以塑性變形導(dǎo)致疲勞剝落磨損為主。在B微合金化基礎(chǔ)上,實(shí)驗(yàn)鋼中分別單獨(dú)加入適量的Ti和RE元素,能夠提高綜合力學(xué)性能,從而一定程度提升耐磨性能。但是,將RE元素加入Ti和B微合金化的實(shí)驗(yàn)鋼中,形成的粗大TiN-稀土夾雜物顆粒,在磨損過程中破碎,造成基體開裂,明顯降低鋼的耐磨性能。(6)在上述材料研究基礎(chǔ)上,結(jié)合實(shí)際工況,制定了大型耐磨襯板選材成分規(guī)范、性能指標(biāo)和全流程生產(chǎn)工藝。并且,采用電弧爐(EAF)-精煉爐(LF)-真空處理(VOD)冶煉技術(shù),通過控制Ti、B和RE加入順序,實(shí)現(xiàn)了自主設(shè)計(jì)中碳低合金鋼耐磨襯板鑄件的批量化生產(chǎn),并且已經(jīng)基本替代進(jìn)口。使用結(jié)果顯示,自主研制的大型耐磨襯板服役壽命達(dá)到75天,現(xiàn)有進(jìn)口服役壽命為65天,提高15.4%。
[Abstract]:In order to improve the production efficiency and reduce the manufacturing cost, the key equipment and its working parts of the iron ore production line are continuously large. Among them, the wear-resistant lining plate is the key equipment of the iron ore powder production line, the core working part of the mill. Its service life directly affects the operation efficiency and manufacturing cost of the whole iron ore production line. However, at present, the domestic iron ore powder production line has a direct effect on the operation efficiency and manufacturing cost. The independent material selection criterion of the super large mill has not been formed. The main key equipment of the super large iron ore production line project in our country depends entirely on the import, resulting in the cost and progress of the project. In order to achieve the expected design life, the material of large wear-resistant parts should have excellent toughness while having high hardness and strength. Therefore, how to obtain good strength and toughness matching and hardenability and further improve the wear resistance of wear resistant steel has always been a subject of great concern for researchers. In this paper, a series of new medium carbon low alloy wear resistant steels have been designed by Ti, B and RE microalloying. The microstructure of Ti, B and RE is analyzed. The type, size and distribution of Ti precipitates and rare earth inclusions in the process of solidification and heat treatment are systematically studied. The wear mechanism of the experimental steel and the relationship between Ti and RE microalloying and the relationship between mechanical properties and wear resistance are discussed. At the same time, the mass production of carbon low alloy steel wear-resistant lining castings in the independent design has been realized. It has accumulated valuable experience for the development of low alloy wear resistant steel materials in China, and laid a solid theoretical foundation for the application of high quality and wear-resistant components. The main contents of this paper include: (1) combined with thermodynamic calculation and experimental research, the paper puts forward the research of the paper. Ti, B and RE microalloying thought: improving hardenability by trace B, adding appropriate Ti and N in steel to ensure B to hardenability, forming TiN precipitate phase, refining microstructure, adding a proper amount of RE (La, Ce), purifying molten steel, improving inclusion and refining grain. By this, a new medium carbon low alloy wear resistant steel alloy system was designed. (2) adoption of a new medium carbon alloy system. (2) The continuous cooling transition (CCT) curve of experimental steel was measured by a thermal expaner. The effect of Ti, B and RE Microalloying on the hardenability was analyzed. The results showed that when B element was added to the experimental steel, B was easily combined with N in steel to form BN, which seriously weakened the effect of hardenability, and the excess B would precipitate the precipitation of M23 (C, B) 6 carbides along the grain boundary. Instead of reducing the hardenability of steel, on this basis, adding a proper amount of Ti elements can effectively fix N, form TiN precipitation phase and inhibit the production of BN, which is beneficial to play a significant role in improving the hardenability of B. However, the addition of RE elements in the experimental steel is mainly combined with O and S in molten steel to form RE203 and RE202S rare earth inclusions, and has no effect on the hardenability of steel. (3) the precipitation behavior of TiN and rare-earth inclusions in the experimental steel and its effect on the solidification structure of the experimental steel were studied by the experiments of thermal insulation solidification and continuous cooling solidification in the solid-liquid two phase region. The results showed that after the isothermal solidification and water quenching, the TiN and the rare earth inclusions in the experimental steel were mainly distributed in the coarse interdendritic interdendrites of the solidified structure and before the dendrites. Along with the finally solidified equiaxed grain boundaries, a small amount is distributed in the coarse dendrites and equiaxed grains of the solidified tissue. The comparison of the low fold microstructure shows that the ratio of the equiaxed grain and the solidification structure can be greatly improved by adding Ti and RE elements. (4) the precipitation characteristics of the precipitated phase and the rare earth impurities in the experimental steel after heat treatment were systematically studied, and Ti, R was discussed. The effect of E content on grain size and mechanical properties showed that, with the increase of Ti content, the particle size of the precipitated phase in the experimental steel increased, the precipitation content increased, the precipitate category gradually changed into micron grade Ti (C, N) and nanoscale (Ti, Mo) (C, N), with obvious dispersion strengthening, fine grain strengthening and ductile plasticity improvement. When Ti content was obtained. At 0.021%, the comprehensive mechanical properties of the experimental steel are the best. As the content of Ti is further increased, the precipitate containing Ti is nucleated at the initial stage and grows rapidly, resulting in a significant increase in the size and precipitation of the precipitated phase, which seriously reduces the impact toughness of the steel. When a proper amount of RE elements is added to the steel, the RE element is combined with O and S in the molten steel. The RE2O3 and RE202S dilute inclusions at 1 m can effectively purify the molten steel and the metamorphic inclusion, and improve the impact toughness of the steel. However, when the RE element and the Ti element are microalloyed with the Ti element, the rare earth inclusions are very easy to be used as the effective core of the TiN in the steel, prompting the TiN and its formation of a larger size and micron grade. The impact toughness is reduced. (5) the wear mechanism of the experimental steel under the impact abrasive wear condition, and the relationship between the microalloying of Ti and RE, the mechanical properties and the wear resistance are discussed by using the MLD-10 dynamic abrasive wear test machine. The experimental results show that the wear surface of the experimental steel in the condition of impact abrasive wear, with the exception of a small amount of display, is shown. On the basis of B microalloying, a proper amount of Ti and RE elements are added separately to the experimental steel on the basis of microalloying, which can improve the comprehensive mechanical properties and improve the wear resistance to a certain extent. However, the RE element is added to the experimental steel of Ti and B microalloying, and the coarse TiN- is formed. The debris particles are broken during the wear process, which causes the matrix cracking and obviously reduces the wear resistance of the steel. (6) on the basis of the research on the above materials, the material material specification, performance index and the whole process production process of the large wear-resistant lining board are formulated on the basis of the above materials, and the EAF refining furnace (LF) vacuum treatment (VOD) smelting technique is adopted. By controlling the order of Ti, B and RE, the mass production of the carbon low alloy steel wear-resistant lining castings in the independent design has been realized, and it has basically replaced the import. The results show that the service life of the self developed large wear-resistant liner has reached 75 days, and the existing import service life is 65 days and 15.4%. is improved.

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG142.72

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